1. Field of the Invention
The present invention relates generally to detecting changes in evoked potentials (EPs), and more particularly to detecting changes in EPs automatically with a computer algorithm.
2. Related Art
Somatosensory evoked potentials are summated electrical potentials usually recorded from the head or neck area after repeatedly stimulating a peripheral nerve. Monitoring patients using somatosensory evoked potentials during surgery has been shown to allow early identification of impending positioning effect injury that can then be avoided by repositioning the patient to alleviate pressure or tension.
For example, as described in Hickey, C.; Gugino, L. D.; Aglio, L. S.; Mark, J. B.; Son, S. L. & Maddi, R. (1993), “Intraoperative somatosensory evoked potential monitoring predicts peripheral nerve injury during cardiac surgery,” Anesthesiology 78(1), 29-35, Kamel, I. R.; Drum, E. T.; Koch, S. A.; Whitten, J. A.; Gaughan, J. P.; Barnette, R. E. & Wendling, W. W. (2006), “The use of somatosensory evoked potentials to determine the relationship between patient positioning and impending upper extremity nerve injury during spine surgery: a retrospective analysis,” Anesth Analg 102(5), 1538-1542, and Labrom, R. D.; Hoskins, M.; Reilly, C. W.; Tredwell, S. J. & Wong, P. K. H. (2005), and “Clinical usefulness of somatosensory evoked potentials for detection of brachial plexopathy secondary to malpositioning in scoliosis surgery.” Spine 30(18), 2089-2093, the above incorporated by reference in their entirety's.
Such monitoring generally requires highly trained technologists under physician supervision with sophisticated, multichannel amplifier and display equipment. Unfortunately, such personnel and equipment are limited in their availability, require pre-booking, and are costly. In addition, such monitoring is not traditionally done in many of the areas in which positioning effects occur outside of the operating room where unresponsive, weak or confined patients may incur positioning effect.
To acquire and record the EPs, a technologist connects electrodes placed on the patient to a neuromonitoring instrument that evokes, acquires, processes and displays the waveforms. Typically, the technologist reviews the waveforms while a neurologist contemporaneously reviews the EP waveforms either on site or remotely through the internet. The technologist and neurologist are trained and are experts in determining whether the changes in the EP waveforms are significant and are indicative of pending nerve injury. The cost of having professionals fully engaged in interpreting these waveforms results in rationing of the service to all but the most high risk surgeries.
U.S. Patent Application Publication No. 2008/0167574 describes a semiautomated device available for automatically measuring biometric signals during surgery to avoid nerve injury. However, the device focuses on muscle or motor recordings to measure nerve proximity to surgical instruments and does not address positioning effect.
The difficulty with analyzing and classifying waveforms to identify positioning effect lies in the wide variation in the amplitude, frequency and shape of the waveforms. These variations are caused by many factors including anesthesia, electrical interference from other devices and any preexisting abnormalities of the nerves.
Accordingly, there is a need for a system and method that can overcome the disadvantages of previous systems and methods.